There is a need for innovative, effective cartilage repair techniques. Limited knowledge of the molecular mechanisms that regulate postnatal chondroblast differentiation (chondroinduction) confounds the design of better repair strategies. This exploratory/developmental project from a New Investigator tests the hypothesis that transcriptional regulator(s) of postnatal chondrogenesis differ from those of prenatal chondrogenesis. The project uses a novel, in vitro system for postnatal chondroinduction that models the conversion of mesenchymal cells into chondroblasts by demineralized bone powder (DBP) in vivo. Human dermal fibroblasts (hDFs) cultured in porous, 3-dimensional collagen sponges with DBP develop a chondroblast phenotype after 7 days, as shown by quantitative biochemical, immunochemical, and gene expression assays for cartilage matrix components. This experimental system is highly relevant to human health, as DBP is used clinically in periodontal, craniomaxillofacial, and orthopedic surgery applications. Previously, we showed that DBP induces specific shifts in gene expression by day 3, prior to full expression of the chondroblast phenotype. The altered expression of several functional classes of genes suggests that DBP activates transcriptional regulators in target cells. Therefore, Specific Aim I is to characterize the expression and activity of transcription factors during postnatal chondroinduction by DBP. Specific genes of interest include transcription factors found to be changed by DBP on day 3 in our Preliminary Studies (ID2, FOG2, MBLL, HBP1), and transcription factors that are known to regulate embryonic chondrogenesis (SOX9, HOXC8, scleraxis). The transcription factor expression profile of postnatal chondrogenesis will be compared to the known patterns of expression during prenatal chondrogenesis. In Specific Aim II, we will determine whether RDA31, a putative zinc-finger protein whose expression is increased in chondroinduced hDFs on day 3, has properties expected of a transcription factor (nuclear localization and transcriptional activator activity). Specific Aim III is to elucidate the transcriptional mechanisms that regulate postnatal chondrogenesis by DBP. We will determine which DBP-regulated transcription factors are necessary and/or sufficient for postnatal chondrogenesis. This proposed work would have a high impact of design of strategies for repair and/or regeneration of cartilage. [unreadable] [unreadable]